A cathode ray tube (CRT) monitor has been gradually replaced by a liquid crystal display (LCD) due to the disadvantages of heavy weight, bulky size, and electromagnetic radiation. So far, an LCD has been extensively applied in various information products and communication products such as a notebook PC, mobile phone, portable PC, personal digital assistant (PDA), and so on. The interface of an information product or a communication product provided for a user to input data, for example, could be a touch panel or touch screen, which is attached on the screen of LCD. Then, the input data is measured by detecting the touch point.
A touch pannel is typically produced by aligning and securely combining an upper substrate and a lower substrate, both of which have good electrical conductivity before being attached onto the LCD panel. The upper substrate and the lower substrate are arranged in parallel and secured to each other with a gap existing therebetween. In other words, the upper substrate does not contact with lower substrate directly, and the gap is kept by providing a set of non-conductive spacer dots glued to and clamped between the upper substrate and the lower substrate. The structure of a touch panel could be one of a “film to film” structure (i.e., the upper substrate and the lower substrate are both conductive films, for example indium-tin oxide (ITO) films), a “film to glass” structure (i.e., the upper substrate and the lower substrate include a conductive film and a conductive glass, for example an ITO film and an ITO glass) and a “glass to glass” structure (i.e., the upper substrate and the lower substrate are both conductive glasses, for example ITO glasses).
Currently, the conductive tracing layout in the touch panel is implemented by printing conductive paste, for example silver paste, on the upper substrate and the lower substrate. Various touch panels have been disclosed in prior art such as Japanese Patent No. JP9026852 entitled “Touch Panel”, and Japanese Patent No. JP60222918 entitled “Manufacture of Touch Type Input Device”, which are incorporated herein for reference.
Please refer to FIG. 1A and FIG. 1B for more details about the conductive tracing layout on the upper substrate and the lower substrate off the touch panel. In FIG. 1A, an example of the conductive tracing layout required by a conventional touch panel is shown. The conventional touch panel 10 mainly includes three areas: an active region 10a, a transparent region 10b and a tracing layout region 10c. The active region 10a is the one where the touch point by an external force can be sensed. The transparent region 10b is of a loop configuration surrounding the active region 10a, and is light-transmissible. The transparent region, on the other hand, has no touch detection function. With regard to tracing layout region 10c, it is also of a loop configuration surrounding the transparent region 10b for providing therein tracing layout required by the touch panel 10. Furthermore, please refer to FIG. 1A, there are four conductive traces 12 disposed on the touch panel 10 and connected to four conductive buses 14 outside the touch panel 10, respectively, which are isolated from one another.
The whole tracing layout shown in FIG. 1A is implemented by separately forming respective portions on the upper and lower substrates, and then gluing the upper and the lower substrates to combine the portions together. FIGS. 1B and 1C schematically show the portions of conductive tracing layout distributed on the upper substrate 20 and the lower substrate 30 of the conventional touch panel, respectively, in other words, while a part of conductive traces 12 are formed on the upper substrate 20, as shown in FIG. 1B, the other part of the conductive traces 12 are formed on the lower substrate 30. By combining the upper substrate 20 and the lower substrate 30 together in parallel, the two portions of conductive traces 12 are combined as the conductive tracing layout shown in FIG. 1A.
Since the above-mentioned conductive tracing layout on the touch panel is achieved in a printing manner that conductive paste is formed on the upper substrate and the lower substrate, there are likely to be some disadvantages as described as follow: (1) relatively large trace width, e.g. larger than 0.5 mm, is required; (2) relatively large line-to-line space, e.g. wider than 0.7 mm, is required due to possible signal loss during signal transmission; and (3) it is hard to narrow down the margins of touch panel, i.e. the distance between the inner and outer edges of the tracing layout region 10C, due to the consideration of adhesion capability of the conductive paste. Generally, the margin of the touch panel is even up to 5.4 mm. Therefore, how to solve these problems will be very important for improving the property of the touch panel.